since hiss is not volume cntrl dependent, you may deal with EMI issue.
adding "Cable Clamp Clip RFI EMI EMC Noise Filters “ to analog bal/unbal cable, close to the amp inputs, sometimes helps.
S/N ratio Balanced input vs. Unbalanced input
Hi, is it normal that signal to noise (S/N) ratio at rated output of balanced input (XLR) is lesser than unbalanced input (RCA) ?
eg. Accuphase E280 , S/N ratio balanced is 96dB, unbalanced is 107dB.
Also E280 , at preamp stage , dB gain : balanced/unbalanced to pre output is 18dB gain, power amp stage dB gain : 28dB, total of 46dB.
What about other integrated amplifiers specs for comparison ?
S/N ratio (balanced) :
S/N ratio (unbalanced):
Preamp gain :
Poweramp gain: